From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C395C2D0BF for ; Tue, 17 Dec 2019 00:52:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA52B24676 for ; Tue, 17 Dec 2019 00:52:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727584AbfLQAwG (ORCPT ); Mon, 16 Dec 2019 19:52:06 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35494 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727166AbfLQAvo (ORCPT ); Mon, 16 Dec 2019 19:51:44 -0500 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1ih15N-0003PI-Nw; Tue, 17 Dec 2019 00:51:37 +0000 Received: from ben by deadeye with local (Exim 4.93-RC7) (envelope-from ) id 1ih15L-0005fS-BE; Tue, 17 Dec 2019 00:51:35 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Al Viro" Date: Tue, 17 Dec 2019 00:47:41 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 127/136] ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.80-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit 762c69685ff7ad5ad7fee0656671e20a0c9c864d upstream. We need to get the underlying dentry of parent; sure, absent the races it is the parent of underlying dentry, but there's nothing to prevent losing a timeslice to preemtion in the middle of evaluation of lower_dentry->d_parent->d_inode, having another process move lower_dentry around and have its (ex)parent not pinned anymore and freed on memory pressure. Then we regain CPU and try to fetch ->d_inode from memory that is freed by that point. dentry->d_parent *is* stable here - it's an argument of ->lookup() and we are guaranteed that it won't be moved anywhere until we feed it to d_add/d_splice_alias. So we safely go that way to get to its underlying dentry. Signed-off-by: Al Viro [bwh: Backported to 3.16: - Open-code d_inode() - Adjust context] Signed-off-by: Ben Hutchings --- fs/ecryptfs/inode.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) --- a/fs/ecryptfs/inode.c +++ b/fs/ecryptfs/inode.c @@ -341,9 +341,9 @@ static int ecryptfs_lookup_interpose(str struct dentry *lower_dentry, struct inode *dir_inode) { + struct path *path = ecryptfs_dentry_to_lower_path(dentry->d_parent); struct inode *inode, *lower_inode; struct ecryptfs_dentry_info *dentry_info; - struct vfsmount *lower_mnt; int rc = 0; dentry_info = kmem_cache_alloc(ecryptfs_dentry_info_cache, GFP_KERNEL); @@ -355,12 +355,11 @@ static int ecryptfs_lookup_interpose(str return -ENOMEM; } - lower_mnt = mntget(ecryptfs_dentry_to_lower_mnt(dentry->d_parent)); - fsstack_copy_attr_atime(dir_inode, lower_dentry->d_parent->d_inode); + fsstack_copy_attr_atime(dir_inode, path->dentry->d_inode); BUG_ON(!d_count(lower_dentry)); ecryptfs_set_dentry_private(dentry, dentry_info); - dentry_info->lower_path.mnt = lower_mnt; + dentry_info->lower_path.mnt = mntget(path->mnt); dentry_info->lower_path.dentry = lower_dentry; /*